The present invention is directed to photosensitive compositions containing rupturable microcapsules.
Photosensitive compositions particularly useful as photoresists are well known in the prior art. Conventionally these compositions are stored in roll form. The composition is adhered to a support film to form a two ply material such as disclosed in Flint, U.S. Pat. No. 4,293,635 or more conventionally in a three ply material such as Celeste. U.S. Pat. No. 3,469,982 with the composition sandwiched between a support film and a cover sheet. The material is unwound from a roll and the cover sheet, if present, is removed from contact with the photosensitive composition prior to use in lamination to a substrate, e.g., in manufacture of printed circuit boards.
The present invention also relates to incorporation of microcapsules in a photosensitive material. Microcapsules such as pressure rupturable microcapsules which have solvent resistant outer walls surrounding active components are known. Several procedures have been described for preparing various types of microcapsules, e.g., Wurster U.S. Pat. No. 2,648,609 (fluidized bed), Vandegaer U.S. Pat. No. 3,577,515 and Ruus U.S. Pat. No. 3,429,827 (interfacial polymerization), Macauley U.S. Pat. No. 3,016,308 (urea/formaldehyde condensation), Green U.S. Pat. No. Re. 24,899 (coacervation), Chao U.S. Pat. No. 4,495,509 (interchange off emulsions). Brynko U.S. Pat. No. 2,969,331 (dual-walled). There are a large number of patents which describe the preparation and use of microcapsules which rupture and release material enclosed by the microcapsule.
Photosensitive materials employing microencapsulated radiation sensitive compositions are the subject of U.S. Pat. Nos. 4,399,209 and 4,440,846 assigned to The Mead Corporation. Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which a blue-black dye is encapsulated with a photocrosslinkable polymer or a photopolymerizable monomer in a film or a layer of discrete microcapsules. Phillips, U.S. Pat. No. 3,700,439, discloses a process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support.
British Patent Publication No. 2,109,331A discloses that microcapsules resistant to solvent action can be prepared with either
(i) at least two prepolymers selected from a melamine/formaldehyde prepolymer, a thiourea/formaldehyde prepolymer and a melamine/thiourea/formaldehyde prepolymer or PA0 (ii) a melamine/thiourea/formaldehyde prepolymer, which are suitable for selective release of color formers in an area where pressure is applied.
Australian Patent No. 25336/84 discloses that microcapsules can be prepared with reduced permeability by treatment of microcapsule walls with a reaction product of formaldehyde and a member from a group of disclosed hydroxylated organic aromatic compounds.
Geissler et al. U.S. Pat. No. 4,438,189 discloses radiation polymerizable mixtures with a concept on the paragraphs bridging columns 3 and 4 of incorporation of crosslinking compounds which are very reactive and soluble in a coating mixture with premature reaction prevented by encapsulating in a covering substance which is insoluble in the coating solvent and which melts or systems below the temperature of subsequent heating for post cure.